1. Field of the Invention
The present invention relates to dye lasers, and in particular, to dye lasers which permit selecting and changing of their output frequency.
2. State of the Art
Dye lasers typically include a lasing medium which circulates through a lasing cavity. The lasing medium in the lasing cavity is excited by an energy source, usually a laser. The lasing medium typically contains a dye which, when excited, radiates at a known frequency or in a known range of frequencies. The output frequency of the laser may be selected by selection of the dye or the concentration of the dye in the lasing medium. An advantageous feature of dye lasers is that the output frequency can be changed by changing the lasing medium.
Changing the lasing medium in the lasing cavity can be time consuming and inconvenient, because it involves removing all of the lasing medium containing the old dye from the laser and replacing it with lasing medium containing the new dye.
Various solutions have been proposed. For example, U.S. Pat. No. 3,745,484 to Caristi discloses a dye laser apparatus having a removable dye module 80 which contains a selected dye solution. U.S. Pat. No. 3,846,715 to Yarborough discloses a dye laser having a plurality of dye reservoirs and circulating systems. A turret assembly provides a means for selecting a dye system and introducing the liquid of that dye system into the laser optical cavity. U.S. Pat. No. 3,868,591 to Mumola et al. discloses a plurality of optical cavities, each supplied with a different lasing fluid, which may be optically pumped by a single light source. U.S. Pat. No. 4,404,679 Chiu et al. discloses a removable sealed dye cell holder. U.S. Pat. No. 4,710,937 to Oomori et al. discloses a dye laser system having a plurality of laser dye vessels each containing a different dye solution which may be optically pumped simultaneously to emit laser beams of different wavelengths.
The lasers described above have disadvantages and limitations which make the selection of a different output frequency difficult or inconvenient. In each of the laser systems mentioned, the stored, or alternative, lasing fluids have the dyes in solution. Once in solution, however, a laser dye degrades, whether the dye is being excited to produce an emission or simply held in storage. Therefore, once prepared, each of the foregoing systems has a limited useful life before refreshing or replacing the lasing medium becomes necessary.
The Yarborough, Mumola, and Oomori patents require different dye vessels or containers for each dye change. This limits the number of dyes which may be contained in the system because of size and other physical constraints, such as coupling each of the various fluid systems to the lasing cavity. As a result, such systems are limited in the range of choices in selecting a dye, and, therefore, the resulting output frequency.
The Caristi and Chiu patents disclose changeable liquid dye cells, which provide the capability for a wide range of dye changes, but are disadvantaged in not being self-contained systems. The user must have on hand a separate dye module or cell for each dye change desired, which can be inconvenient if the laser is to be used in the field.